Increasing CSI-RS overhead via antenna port augmentation

ABSTRACT

A method of wireless communication is presented. The method includes signaling a first number of channel state information-reference signal (CSI-RS) ports corresponding to resource elements (REs) and a second number of virtual antenna ports, the second number being less than or equal to the first number. The method also includes transmitting CSI-RS on each virtual antenna port, the CSI-RS mapped to at least a portion of the REs.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 61/542,766 entitled “INCREASINGCHANNEL STATE INFORMATION-REFERENCE SIGNAL OVERHEAD THROUGH ANTENNAPORTS AUGMENTATION,” filed on Oct. 3, 2011, the disclosure of which isexpressly incorporated by reference herein in its entirety.

BACKGROUND

1. Field

Aspects of the present disclosure relate generally to wirelesscommunication systems, and more particularly to increasing channel stateinformation-reference signal (CSI-RS) overhead via antenna portaugmentation.

2. Background

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power). Examples of such multiple-access technologies includecode division multiple access (CDMA) systems, time division multipleaccess (TDMA) systems, frequency division multiple access (FDMA)systems, orthogonal frequency division multiple access (OFDMA) systems,single-carrier frequency divisional multiple access (SC-FDMA) systems,and time division synchronous code division multiple access (TD-SCDMA)systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example of an emergingtelecommunication standard is Long Term Evolution (LTE). LTE is a set ofenhancements to the Universal Mobile Telecommunications System (UMTS)mobile standard promulgated by Third Generation Partnership Project(3GPP). It is designed to better support mobile broadband Internetaccess by improving spectral efficiency, lower costs, improve services,make use of new spectrum, and better integrate with other open standardsusing OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), andmultiple-input multiple-output (MIMO) antenna technology. However, asthe demand for mobile broadband access continues to increase, thereexists a need for further improvements in LTE technology. Preferably,these improvements should be applicable to other multi-accesstechnologies and the telecommunication standards that employ thesetechnologies.

This has outlined, rather broadly, the features and technical advantagesof the present disclosure in order that the detailed description thatfollows may be better understood. Additional features and advantages ofthe disclosure will be described below. It should be appreciated bythose skilled in the art that this disclosure may be readily utilized asa basis for modifying or designing other structures for carrying out thesame purposes of the present disclosure. It should also be realized bythose skilled in the art that such equivalent constructions do notdepart from the teachings of the disclosure as set forth in the appendedclaims. The novel features, which are believed to be characteristic ofthe disclosure, both as to its organization and method of operation,together with further objects and advantages, will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present disclosure.

SUMMARY

According to an aspect of the present disclosure, a method of wirelesscommunication is presented. The method includes signaling a first numberof channel state information-reference signal (CSI-RS) portscorresponding to resource elements (REs). The method also includessignaling a second number of virtual antenna ports, the second numberbeing less than or equal to the first number. The method furtherincludes transmitting CSI-RS on each virtual antenna port, the CSI-RSmapped to at least a portion of the REs.

According to another aspect, a method of wireless communication ispresented. The method includes receiving a first number of CSI-RS portscorresponding to REs. The method also includes. The method also includesreceiving a second number of virtual antenna ports, the second numberbeing less than or equal to the first number. The method furtherincludes receiving CSI-RS on each virtual antenna port, the CSI-RSmapping to at least a portion of the REs.

According to yet another aspect, an apparatus for wireless communicationis presented. The apparatus includes means for signaling a first numberof CSI-RS ports corresponding to REs. The apparatus also includes meansfor signaling a second number of virtual antenna ports, the secondnumber being less than or equal to the first number. The apparatusfurther includes means for transmitting CSI-RS on each virtual antennaport, the CSI-RS mapped to at least a portion of the REs.

According to still yet another aspect, an apparatus for wirelesscommunication is presented. The apparatus includes means for receiving afirst number of CSI-RS ports corresponding to REs. The apparatus alsoincludes means for receiving a second number of virtual antenna ports,the second number being less than or equal to the first number. Theapparatus further includes means for receiving CSI-RS on each virtualantenna port, the CSI-RS mapping to at least a portion of the REs.

According to another aspect, a computer program product for wirelesscommunication in a wireless network. The computer program productincludes a non-transitory computer-readable medium having non-transitoryprogram code recorded thereon. The program code includes program code tosignal a first number of CSI-RS ports corresponding to REs. The programcode also includes program code to signal a second number of virtualantenna ports, the second number being less than or equal to the firstnumber. The program code further includes program code to transmitCSI-RS on each virtual antenna port, the CSI-RS mapped to at least aportion of the REs.

According to yet another aspect, computer program product for wirelesscommunication in a wireless network is presented. The computer programproduct includes a non-transitory computer-readable medium havingnon-transitory program code recorded thereon. The program code includesprogram code to receive a first number of channel stateinformation-reference signal (CSI-RS) ports corresponding to resourceelements (REs). The program code also includes program code to receive asecond number of virtual antenna ports, the second number being lessthan or equal to the first number. The program code further includesprogram code to receive CSI-RS on each virtual antenna port, the CSI-RSmapping to at least a portion of the REs.

According to still yet another aspect, an apparatus for wirelesscommunication is presented. The apparatus includes a memory and at leastone processor coupled to the memory. The processor(s) is configured tosignal a first number of channel state information-reference signal(CSI-RS) ports corresponding to resource elements (REs). Theprocessor(s) also being configured to signal a second number of virtualantenna ports, the second number being less than or equal to the firstnumber. The processor(s) further being configured to transmit CSI-RS oneach virtual antenna port, the CSI-RS mapped to at least a portion ofthe REs.

According to another aspect, an apparatus for wireless communication ispresented. The apparatus includes a memory and at least one processorcoupled to the memory. The processor(s) is configured to receive a firstnumber of channel state information-reference signal (CSI-RS) portscorresponding to resource elements (REs). The processor(s) is alsoconfigured to receive a second number of virtual antenna ports, thesecond number being less than or equal to the first number. Theprocessor(s) is further configured to receive CSI-RS on each virtualantenna port, the CSI-RS mapping to at least a portion of the REs.

Additional features and advantages of the disclosure will be describedbelow. It should be appreciated by those skilled in the art that thisdisclosure may be readily utilized as a basis for modifying or designingother structures for carrying out the same purposes of the presentdisclosure. It should also be realized by those skilled in the art thatsuch equivalent constructions do not depart from the teachings of thedisclosure as set forth in the appended claims. The novel features,which are believed to be characteristic of the disclosure, both as toits organization and method of operation, together with further objectsand advantages, will be better understood from the following descriptionwhen considered in connection with the accompanying figures. It is to beexpressly understood, however, that each of the figures is provided forthe purpose of illustration and description only and is not intended asa definition of the limits of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present disclosure willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout.

FIG. 1 is a diagram illustrating an example of a network architecture.

FIG. 2 is a diagram illustrating an example of an access network.

FIG. 3 is a diagram illustrating an example of a downlink framestructure in LTE.

FIG. 4 is a diagram illustrating an example of an uplink frame structurein LTE.

FIG. 5 is a diagram illustrating an example of a radio protocolarchitecture for the user and control plane.

FIG. 6 is a diagram illustrating an example of an evolved Node B anduser equipment in an access network.

FIG. 7 is a block diagram illustrating examples of CSI-RS allocation ina conventional LTE system.

FIGS. 8A and 8B are block diagrams illustrating methods for increasingCSI-RS overhead via antenna port augmentation.

FIG. 9 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an exemplary apparatus.

FIG. 10 is a block diagram illustrating differentmodules/means/components in an exemplary apparatus.

FIG. 11 is a block diagram illustrating differentmodules/means/components in an exemplary apparatus.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with theappended drawings, is intended as a description of variousconfigurations and is not intended to represent the only configurationsin which the concepts described herein may be practiced. The detaileddescription includes specific details for the purpose of providing athorough understanding of the various concepts. However, it will beapparent to those skilled in the art that these concepts may bepracticed without these specific details. In some instances, well-knownstructures and components are shown in block diagram form in order toavoid obscuring such concepts.

Aspects of the telecommunication systems are presented with reference tovarious apparatus and methods. These apparatus and methods are describedin the following detailed description and illustrated in theaccompanying drawings by various blocks, modules, components, circuits,steps, processes, algorithms, etc. (collectively referred to as“elements”). These elements may be implemented using electronichardware, computer software, or any combination thereof. Whether suchelements are implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented with a “processing system”that includes one or more processors. Examples of processors includemicroprocessors, microcontrollers, digital signal processors (DSPs),field programmable gate arrays (FPGAs), programmable logic devices(PLDs), state machines, gated logic, discrete hardware circuits, andother suitable hardware configured to perform the various functionalitydescribed throughout this disclosure. One or more processors in theprocessing system may execute software. Software shall be construedbroadly to mean instructions, instruction sets, code, code segments,program code, programs, subprograms, software modules, applications,software applications, software packages, routines, subroutines,objects, executables, threads of execution, procedures, functions, etc.,whether referred to as software, firmware, middleware, microcode,hardware description language, or otherwise.

Accordingly, in one or more exemplary embodiments, the functionsdescribed may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the functions may bestored on or encoded as one or more instructions or code on acomputer-readable medium. Computer-readable media includes computerstorage media. Storage media may be any available media that can beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code in the form of instructions or data structures and that canbe accessed by a computer. Disk and disc, as used herein, includescompact disc (CD), laser disc, optical disc, digital versatile disc(DVD), floppy disk and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

FIG. 1 is a diagram illustrating an LTE network architecture 100. TheLTE network architecture 100 may be referred to as an Evolved PacketSystem (EPS) 100. The EPS 100 may include one or more user equipment(UE) 102, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN)104, an Evolved Packet Core (EPC) 110, a Home Subscriber Server (HSS)120, and an Operator's IP Services 122. The EPS can interconnect withother access networks, but for simplicity, those entities/interfaces arenot shown. As shown, the EPS provides packet-switched services, however,as those skilled in the art will readily appreciate, the variousconcepts presented throughout this disclosure may be extended tonetworks providing circuit-switched services.

The E-UTRAN includes the evolved Node B (eNodeB) 106 and other eNodeBs108. The eNodeB 106 provides user and control plane protocolterminations toward the UE 102. The eNodeB 106 may be connected to theother eNodeBs 108 via a backhaul (e.g., an X2 interface). The eNodeB 106may also be referred to as a base station, a base transceiver station, aradio base station, a radio transceiver, a transceiver function, a basicservice set (BSS), an extended service set (ESS), or some other suitableterminology. The eNodeB 106 provides an access point to the EPC 110 fora UE 102. Examples of UEs 102 include a cellular phone, a smart phone, asession initiation protocol (SIP) phone, a laptop, a personal digitalassistant (PDA), a satellite radio, a global positioning system, amultimedia device, a video device, a digital audio player (e.g., MP3player), a camera, a game console, or any other similar functioningdevice. The UE 102 may also be referred to by those skilled in the artas a mobile station, a subscriber station, a mobile unit, a subscriberunit, a wireless unit, a remote unit, a mobile device, a wirelessdevice, a wireless communications device, a remote device, a mobilesubscriber station, an access terminal, a mobile terminal, a wirelessterminal, a remote terminal, a handset, a user agent, a mobile client, aclient, or some other suitable terminology.

The eNodeB 106 is connected to the EPC 110 via, e.g., an S1 interface.The EPC 110 includes a Mobility Management Entity (MME) 112, other MMEs114, a Serving Gateway 116, and a Packet Data Network (PDN) Gateway 118.The MME 112 is the control node that processes the signaling between theUE 102 and the EPC 110. Generally, the MME 112 provides bearer andconnection management. All user IP packets are transferred through theServing Gateway 116, which itself is connected to the PDN Gateway 118.The PDN Gateway 118 provides UE IP address allocation as well as otherfunctions. The PDN Gateway 118 is connected to the Operator's IPServices 122. The Operator's IP Services 122 may include the Internet,the Intranet, an IP Multimedia Subsystem (IMS), and a PS StreamingService (PSS).

FIG. 2 is a diagram illustrating an example of an access network 200 inan LTE network architecture. In this example, the access network 200 isdivided into a number of cellular regions (cells) 202. One or more lowerpower class eNodeBs 208 may have cellular regions 210 that overlap withone or more of the cells 202. The lower power class eNodeB 208 may be aremote radio head (RRH), a femto cell (e.g., home eNodeB (HeNodeB)),pico cell, or micro cell. The macro eNodeBs 204 are each assigned to arespective cell 202 and are configured to provide an access point to theEPC 110 for all the UEs 206 in the cells 202. There is no centralizedcontroller in this example of an access network 200, but a centralizedcontroller may be used in alternative configurations. The eNodeBs 204are responsible for all radio related functions including radio bearercontrol, admission control, mobility control, scheduling, security, andconnectivity to the serving gateway 116.

The modulation and multiple access scheme employed by the access network200 may vary depending on the particular telecommunications standardbeing deployed. In LTE applications, OFDM is used on the downlink andSC-FDMA is used on the uplink to support both frequency divisionduplexing (FDD) and time division duplexing (TDD). As those skilled inthe art will readily appreciate from the detailed description to follow,the various concepts presented herein are well suited for LTEapplications. However, these concepts may be readily extended to othertelecommunication standards employing other modulation and multipleaccess techniques. By way of example, these concepts may be extended toEvolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB). EV-DOand UMB are air interface standards promulgated by the 3rd GenerationPartnership Project 2 (3GPP2) as part of the CDMA2000 family ofstandards and employs CDMA to provide broadband Internet access tomobile stations. These concepts may also be extended to UniversalTerrestrial Radio Access (UTRA) employing Wideband-CDMA (W-CDMA) andother variants of CDMA, such as TD-SCDMA; Global System for MobileCommunications (GSM) employing TDMA; and Evolved UTRA (E-UTRA), UltraMobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, and Flash-OFDM employing OFDMA. UTRA, E-UTRA, UMTS, LTE and GSMare described in documents from the 3GPP organization. CDMA2000 and UMBare described in documents from the 3GPP2 organization. The actualwireless communication standard and the multiple access technologyemployed will depend on the specific application and the overall designconstraints imposed on the system.

The eNodeBs 204 may have multiple antennas supporting MIMO technology.The use of MIMO technology enables the eNodeBs 204 to exploit thespatial domain to support spatial multiplexing, beamforming, andtransmit diversity. Spatial multiplexing may be used to transmitdifferent streams of data simultaneously on the same frequency. The datasteams may be transmitted to a single UE 206 to increase the data rateor to multiple UEs 206 to increase the overall system capacity. This isachieved by spatially precoding each data stream (i.e., applying ascaling of an amplitude and a phase) and then transmitting eachspatially precoded stream through multiple transmit antennas on thedownlink. The spatially precoded data streams arrive at the UE(s) 206with different spatial signatures, which enables each of the UE(s) 206to recover the one or more data streams destined for that UE 206. On theuplink, each UE 206 transmits a spatially precoded data stream, whichenables the eNodeB 204 to identify the source of each spatially precodeddata stream.

Spatial multiplexing is generally used when channel conditions are good.When channel conditions are less favorable, beamforming may be used tofocus the transmission energy in one or more directions. This may beachieved by spatially precoding the data for transmission throughmultiple antennas. To achieve good coverage at the edges of the cell, asingle stream beamforming transmission may be used in combination withtransmit diversity.

In the detailed description that follows, various aspects of an accessnetwork will be described with reference to a MIMO system supportingOFDM on the downlink. OFDM is a spread-spectrum technique that modulatesdata over a number of subcarriers within an OFDM symbol. The subcarriersare spaced apart at precise frequencies. The spacing provides“orthogonality” that enables a receiver to recover the data from thesubcarriers. In the time domain, a guard interval (e.g., cyclic prefix)may be added to each OFDM symbol to combat inter-OFDM-symbolinterference. The uplink may use SC-FDMA in the form of a DFT-spreadOFDM signal to compensate for high peak-to-average power ratio (PAPR).

FIG. 3 is a diagram 300 illustrating an example of a downlink framestructure in LTE. A frame (10 ms) may be divided into 10 equally sizedsub-frames. Each sub-frame may include two consecutive time slots. Aresource grid may be used to represent two time slots, each time slotincluding a resource block. The resource grid is divided into multipleresource elements. In LTE, a resource block contains 12 consecutivesubcarriers in the frequency domain and, for a normal cyclic prefix ineach OFDM symbol, 7 consecutive OFDM symbols in the time domain, or 84resource elements. For an extended cyclic prefix, a resource blockcontains 6 consecutive OFDM symbols in the time domain and has 72resource elements. Some of the resource elements, as indicated as R 302,304, include downlink reference signals (DL-RS). The DL-RS includeCell-specific RS (CRS) (also sometimes called common RS) 302 andUE-specific RS (UE-RS) 304. UE-RS 304 are transmitted only on theresource blocks upon which the corresponding physical downlink sharedchannel (PDSCH) is mapped. The number of bits carried by each resourceelement depends on the modulation scheme. Thus, the more resource blocksthat a UE receives and the higher the modulation scheme, the higher thedata rate for the UE.

FIG. 4 is a diagram 400 illustrating an example of an uplink framestructure in LTE. The available resource blocks for the uplink may bepartitioned into a data section and a control section. The controlsection may be formed at the two edges of the system bandwidth and mayhave a configurable size. The resource blocks in the control section maybe assigned to UEs for transmission of control information. The datasection may include all resource blocks not included in the controlsection. The uplink frame structure results in the data sectionincluding contiguous subcarriers, which may allow a single UE to beassigned all of the contiguous subcarriers in the data section.

A UE may be assigned resource blocks 410 a, 410 b in the control sectionto transmit control information to an eNodeB. The UE may also beassigned resource blocks 420 a, 420 b in the data section to transmitdata to the eNodeB. The UE may transmit control information in aphysical uplink control channel (PUCCH) on the assigned resource blocksin the control section. The UE may transmit only data or both data andcontrol information in a physical uplink shared channel (PUSCH) on theassigned resource blocks in the data section. An uplink transmission mayspan both slots of a subframe and may hop across frequency.

A set of resource blocks may be used to perform initial system accessand achieve uplink synchronization in a physical random access channel(PRACH) 430. The PRACH 430 carries a random sequence and cannot carryany uplink data/signaling. Each random access preamble occupies abandwidth corresponding to six consecutive resource blocks. The startingfrequency is specified by the network. That is, the transmission of therandom access preamble is restricted to certain time and frequencyresources. There is no frequency hopping for the PRACH. The PRACHattempt is carried in a single subframe (1 ms) or in a sequence of fewcontiguous subframes and a UE can make only a single PRACH attempt perframe (10 ms).

FIG. 5 is a diagram 500 illustrating an example of a radio protocolarchitecture for the user and control planes in LTE. The radio protocolarchitecture for the UE and the eNodeB is shown with three layers: Layer1, Layer 2, and Layer 3. Layer 1 (L1 layer) is the lowest layer andimplements various physical layer signal processing functions. The L1layer will be referred to herein as the physical layer 506. Layer 2 (L2layer) 508 is above the physical layer 506 and is responsible for thelink between the UE and eNodeB over the physical layer 506.

In the user plane, the L2 layer 508 includes a media access control(MAC) sublayer 510, a radio link control (RLC) sublayer 512, and apacket data convergence protocol (PDCP) 514 sublayer, which areterminated at the eNodeB on the network side. Although not shown, the UEmay have several upper layers above the L2 layer 508 including a networklayer (e.g., IP layer) that is terminated at the PDN gateway 118 on thenetwork side, and an application layer that is terminated at the otherend of the connection (e.g., far end UE, server, etc.).

The PDCP sublayer 514 provides multiplexing between different radiobearers and logical channels. The PDCP sublayer 514 also provides headercompression for upper layer data packets to reduce radio transmissionoverhead, security by ciphering the data packets, and handover supportfor UEs between eNodeBs. The RLC sublayer 512 provides segmentation andreassembly of upper layer data packets, retransmission of lost datapackets, and reordering of data packets to compensate for out-of-orderreception due to hybrid automatic repeat request (HARQ). The MACsublayer 510 provides multiplexing between logical and transportchannels. The MAC sublayer 510 is also responsible for allocating thevarious radio resources (e.g., resource blocks) in one cell among theUEs. The MAC sublayer 510 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE andeNodeB is substantially the same for the physical layer 506 and the L2layer 508 with the exception that there is no header compressionfunction for the control plane. The control plane also includes a radioresource control (RRC) sublayer 516 in Layer 3 (L3 layer). The RRCsublayer 516 is responsible for obtaining radio resources (i.e., radiobearers) and for configuring the lower layers using RRC signalingbetween the eNodeB and the UE.

FIG. 6 is a block diagram of an eNodeB 610 in communication with a UE650 in an access network. In the downlink, upper layer packets from thecore network are provided to a controller/processor 675. Thecontroller/processor 675 implements the functionality of the L2 layer.In the downlink, the controller/processor 675 provides headercompression, ciphering, packet segmentation and reordering, multiplexingbetween logical and transport channels, and radio resource allocationsto the UE 650 based on various priority metrics. Thecontroller/processor 675 is also responsible for HARQ operations,retransmission of lost packets, and signaling to the UE 650.

The TX processor 616 implements various signal processing functions forthe L1 layer (i.e., physical layer). The signal processing functionsincludes coding and interleaving to facilitate forward error correction(FEC) at the UE 650 and mapping to signal constellations based onvarious modulation schemes (e.g., binary phase-shift keying (BPSK),quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK),M-quadrature amplitude modulation (M-QAM)). The coded and modulatedsymbols are then split into parallel streams. Each stream is then mappedto an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot)in the time and/or frequency domain, and then combined together using anInverse Fast Fourier Transform (IFFT) to produce a physical channelcarrying a time domain OFDM symbol stream. The OFDM stream is spatiallyprecoded to produce multiple spatial streams. Channel estimates from achannel estimator 674 may be used to determine the coding and modulationscheme, as well as for spatial processing. The channel estimate may bederived from a reference signal and/or channel condition feedbacktransmitted by the UE 650. Each spatial stream is then provided to adifferent antenna 620 via a separate transmitter 618TX. Each transmitter618TX modulates an RF carrier with a respective spatial stream fortransmission.

At the UE 650, each receiver 654RX receives a signal through itsrespective antenna 652. Each receiver 654RX recovers informationmodulated onto an RF carrier and provides the information to thereceiver (RX) processor 656. The RX processor 656 implements varioussignal processing functions of the L1 layer. The RX processor 656performs spatial processing on the information to recover any spatialstreams destined for the UE 650. If multiple spatial streams aredestined for the UE 650, they may be combined by the RX processor 656into a single OFDM symbol stream. The RX processor 656 then converts theOFDM symbol stream from the time-domain to the frequency domain using aFast Fourier Transform (FFT). The frequency domain signal comprises aseparate OFDM symbol stream for each subcarrier of the OFDM signal. Thesymbols on each subcarrier, and the reference signal, is recovered anddemodulated by determining the most likely signal constellation pointstransmitted by the eNodeB 610. These soft decisions may be based onchannel estimates computed by the channel estimator 658. The softdecisions are then decoded and deinterleaved to recover the data andcontrol signals that were originally transmitted by the eNodeB 610 onthe physical channel. The data and control signals are then provided tothe controller/processor 659.

The controller/processor 659 implements the L2 layer. Thecontroller/processor 659 can be associated with a memory 660 that storesprogram codes and data. The memory 660 may be referred to as acomputer-readable medium. In the uplink, the controller/processor 659provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the core network. The upper layerpackets are then provided to a data sink 662, which represents all theprotocol layers above the L2 layer. Various control signals may also beprovided to the data sink 662 for L3 processing. Thecontroller/processor 659 is also responsible for error detection usingan acknowledgement (ACK) and/or negative acknowledgement (NACK) protocolto support HARQ operations.

In the uplink, a data source 667 is used to provide upper layer packetsto the controller/processor 659. The data source 667 represents allprotocol layers above the L2 layer. Similar to the functionalitydescribed in connection with the downlink transmission by the eNodeB610, the controller/processor 659 implements the L2 layer for the userplane and the control plane by providing header compression, ciphering,packet segmentation and reordering, and multiplexing between logical andtransport channels based on radio resource allocations by the eNodeB610. The controller/processor 659 is also responsible for HARQoperations, retransmission of lost packets, and signaling to the eNodeB610.

Channel estimates derived by a channel estimator 658 from a referencesignal or feedback transmitted by the eNodeB 610 may be used by the TXprocessor 668 to select the appropriate coding and modulation schemes,and to facilitate spatial processing. The spatial streams generated bythe TX processor 668 are provided to different antenna 652 via separatetransmitters 654TX. Each transmitter 654TX modulates an RF carrier witha respective spatial stream for transmission.

The uplink transmission is processed at the eNodeB 610 in a mannersimilar to that described in connection with the receiver function atthe UE 650. Each receiver 618RX receives a signal through its respectiveantenna 620. Each receiver 618RX recovers information modulated onto anRF carrier and provides the information to a RX processor 670. The RXprocessor 670 may implement the L1 layer.

The controller/processor 675 implements the L2 layer. Thecontroller/processor 675 can be associated with a memory 676 that storesprogram codes and data. The memory 676 may be referred to as acomputer-readable medium. In the uplink, the controller/processor 675provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the UE 650. Upper layer packets fromthe controller/processor 675 may be provided to the core network. Thecontroller/processor 675 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

Increasing CSI-RS Overhead Via Antenna Port Augmentation

In LTE Release 8, 9, and 10, channel state information-reference signal(CSI-RS) overhead is maintained at a low level. That is, in each of thesubframes that transmit CSI-RS, one resource element (RE) per resourceblock is associated with an antenna port for each CSI-RS configuration.

The CSI-RS patterns defined for LTE Release 8, 9, and 10 are shown inFIG. 7. As shown in FIG. 7, the X-axis designates time and the Y-axisdesignates frequency. Each block corresponds to a resource element andthe hatched resource elements are allocated to the CSI-RS antenna ports.Furthermore, as shown in FIG. 7, two resource elements are allocated tothe CSI-RS antenna ports when the eNodeB designates two CSI-RS antennaports. Moreover, four resource elements are allocated to the CSI-RSantenna ports when the eNodeB designates four CSI-RS antenna ports andeight resource elements are allocated to the CSI-RS antenna ports whenthe eNodeB designates eight CSI-RS antenna ports.

The CSI-RS overhead of conventional LTE systems may not be desirable insome scenarios. For example, when performing CSI-RS interferencecancellation (CSI-RS-IC), a UE may determine an estimate of the fadingchannel from the interferer. If the channel estimation is below athreshold, i.e., not accurate, the performance of interferencecancellation may be decreased. The conventional CSI-RS overhead providesfor a channel estimation that is below a threshold for providingreliable CSI-RS interference cancellation.

Furthermore, reliable channel estimation of the interference covariancematrix specifies a greater amount of CSI-RS averaging in comparison tothe averaging specified for a typical channel estimation. Thus, thenumber of resource elements allocated to CSI-RS for each slot in aconventional LTE system may not be adequate for providing a reliablechannel estimate. Therefore, it is desirable to provide CSI-RSconfigurations with an increased overhead for the UE to improve channelestimations.

Typically, the number of resource elements for each CSI-RS configurationdepends on the number of CSI-RS antenna ports specified by the eNodeB.The number of antenna ports specified by the eNodeB may be differentfrom the number of physical antennas and/or the number of CRS antennaports. According to an aspect of the present disclosure, the eNodeB mayincrease the number of CSI-RS antenna ports declared to increase theavailable CSI-RS resource elements.

In one aspect of the present disclosure, the eNodeB may declare multipleCSI-RS antenna ports so that the number of declared CSI-RS antenna portsis greater than the number of physical antennas. For example, the eNodeBmay declare eight CSI-RS antenna ports, which is the maximum number ofantenna ports according to the LTE Release 10 specification. In thisexample, as a result of declaring the maximum number of CSI-RS antennaports according to the LTE standard, more resource elements may beallocated for the CSI-RS.

The eNodeB may transmit antenna information to the UE via a signal, suchas a radio resource control (RRC) signal. The antenna information mayinform the UE of the number of CSI-RS antenna ports and the number ofvirtual antenna ports to be assumed by the UE for channel estimation.The virtual antenna ports may be equal to or less than the total numberof CSI-RS antenna ports. LTE Release 10 specifies an information elementfor informing the UE of the number of CSI-RS antenna ports. Thus,according to an aspect, an additional information element may bespecified for informing the UE of the virtual antenna port information.

The eNodeB transmits the CSI-RS on the virtual antenna ports. Therefore,the eNodeB and UE agree to a mapping between the CSI-RS antenna portsand the virtual antenna ports. The mapping may be agreed via rulesspecified in the standard. The resource elements associated with eachvirtual antenna port will all have the same CSI-RS information.Therefore, the UE may use the mapping to determine how many resourceelements will be allocated to the identical CSI-RS information. That is,the UE determines the correlation between the resource elements and thevirtual antenna ports.

For example, when an eNodeB specifies two virtual antenna ports andeight CSI-RS antenna ports, the first virtual antenna port may be mappedto the even-numbered CSI-RS antenna ports and the second virtual antennaport may be mapped to the odd-numbered CSI-RS antenna ports. Because theeNodeB transmits the CSI-RS via the virtual antenna ports, in thepresent example, the UE may receive four of the same CSI-RSs on each ofthe two virtual ports.

In the present disclosure, an advanced UE may perform channel estimationand/or measure interference via the joint processing of resourceelements allocated to different CSI-RS antenna ports mapped to the samevirtual antenna port. Because all CSI-RS resource elements of a virtualport carry identical information, the UE may use all of the resourceelements to increase the reliability of the channel estimation and/orinterference measurements. Joint processing may refer to averagingresource elements or increasing frequency and/or time resolution.Alternatively, joint processing may also refer to a statistical functionfor processing multiple resource elements to perform channel and/orinterference estimations. The increase in frequency or time resolutionmay be limited because an increased processing gain is specified tofacilitate CRS-IC.

When the CSI evaluations are based on the CSI-RS, the UE assumes thatthe number of antennas is equal to the number of virtual antenna ports.Furthermore, the CSI may include a pre-coding matrix index (PMI) basedon a codebook associated with the number of virtual antenna ports.

Legacy UEs may still use the same CSI-RS resources. Still, the eNodeBmay signal different configurations to the legacy UEs. In some cases,the legacy UE may receive a configuration for CSI-RS antenna ports andanother configuration for a muting pattern. As an example, the eNodeBmay specify two virtual antenna ports and eight CSI-RS antenna ports. Inthis example, the legacy UE may receive signaling for two CSI-RS portsand an overlapping eight CSI-RS muting pattern. The muting pattern isbased on the CSI-RS ports. Thus, the legacy UE may perform channelestimation based on the two CSI-RS ports. Still, the legacy UE may notuse resource element averaging or enhanced interference estimation forthe channel estimation.

Although CSI-RS is primarily associated with transmission mode 9,aspects of the present disclosure are also contemplated for a UEconfigured with transmission modes 1, 2, 3, 4, 5, 6, 7, and 8, whilealso being configured to use CSI-RS for channel estimation and/or CSI-RSresources for interference estimation. It should be noted that LTEReleases 8,9, and 10 specify for transmission modes 1, 2, 3, 4, 5, 6, 7,8 to use CRS-based channel and/or interference estimation. Thus, theaspects of the present disclosure may not be compatible withconventional LTE systems.

FIG. 8A illustrates a method 800 for increasing CSI-RS overhead viaantenna port augmentation. In block 802, a base station signals a firstnumber of CSI-RS ports corresponding to the resource elements (REs). Thebase station signals a second number of virtual antenna ports, thesecond number is less than or equal to the first number, in block 804.Furthermore, the base station transmits CSI-RS on each virtual antennaport, where the CSI-RS is mapped to at least a portion of the REs, inblock 806.

FIG. 8B illustrates a method 801 for increasing CSI-RS overhead viaantenna port augmentation. In block 808, a mobile station receives afirst number of CSI-RS ports corresponding to the resource elements(REs). The mobile station receives a second number of virtual antennaports, the second number being less than or equal to the first number,in block 810. Furthermore, the mobile station receives CSI-RS on eachvirtual antenna port, the CSI-RS mapping to at least a portion of theREs, in block 812.

In one configuration, the eNodeB 610 is configured for wirelesscommunication including means for signaling and means for transmitting.In one aspect, the signaling and transmitting means may be thecontroller/processor 675, transmit processor 616, modulators 618, andantenna 620 configured to perform the functions recited by the signalingmeans and transmitting means. In another aspect, the aforementionedmeans may be any module or any apparatus configured to perform thefunctions recited by the aforementioned means.

In one configuration, the UE 650 is configured for wirelesscommunication including means for receiving. In one aspect, thereceiving means may be the controller/processor 659, memory 660; receiveprocessor 656, modulators 654, antenna 652) configured to perform thefunctions recited by the receiving means. In another aspect, theaforementioned means may be any module or any apparatus configured toperform the functions recited by the aforementioned means.

FIG. 9 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an exemplary apparatus900. The apparatus 900 includes a mapping module 902 that signals afirst number of CSI-RS ports corresponding to REs. The mapping module902 also signals a second number of virtual antenna ports, the secondnumber being less than or equal to the first number. The mapping module902 transmits the signals via a transmission module 908. Thetransmission module 908 may transmit the signals from the mapping modulevia a signal 912. The transmission module 908 may further transmitsCSI-RS on each virtual antenna port via the signal 912. The apparatusmay include additional modules that perform each of the steps of thealgorithm in the aforementioned flow chart FIG. 8A. As such, each stepin the aforementioned flow chart FIG. 8A may be performed by a moduleand the apparatus may include one or more of those modules. The modulesmay be one or more hardware components specifically configured to carryout the stated processes/algorithm, implemented by a processorconfigured to perform the stated processes/algorithm, stored within acomputer-readable medium for implementation by a processor, or somecombination thereof.

FIG. 10 is a diagram illustrating an example of a hardwareimplementation for an apparatus 1000 employing a processing system 1014.The processing system 1014 may be implemented with a bus architecture,represented generally by the bus 1024. The bus 1024 may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system 1014 and the overall designconstraints. The bus 1024 links together various circuits including oneor more processors and/or hardware modules, represented by the processor1022 the modules 1002, 1004, and the computer-readable medium 1026. Thebus 1024 may also link various other circuits such as timing sources,peripherals, voltage regulators, and power management circuits, whichare well known in the art, and therefore, will not be described anyfurther.

The apparatus includes a processing system 1014 coupled to a transceiver1030. The transceiver 1030 is coupled to one or more antennas 1020. Thetransceiver 1030 enables communicating with various other apparatus overa transmission medium. The processing system 1014 includes a processor1022 coupled to a computer-readable medium 1026. The processor 1022 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium 1026. The software, when executedby the processor 1022, causes the processing system 1014 to perform thevarious functions described for any particular apparatus. Thecomputer-readable medium 1026 may also be used for storing data that ismanipulated by the processor 1022 when executing software.

The processing system 1014 includes a signaling module 1002 forsignaling a first number of CSI-RS ports corresponding to REs. Thesignaling module 1002 also signals a second number of virtual antennaports, the second number being less than or equal to the first number.The processing system 1014 also includes a transmission module 1004 fortransmitting CSI-RS on each virtual antenna port. The modules may besoftware modules running in the processor 1022, resident/stored in thecomputer-readable medium 1026, one or more hardware modules coupled tothe processor 1022, or some combination thereof The processing system1014 may be a component of the eNodeB 610 and may include the memory676, and/or the controller/processor 675.

FIG. 11 is a diagram illustrating an example of a hardwareimplementation for an apparatus 1100 employing a processing system 1114.The processing system 1114 may be implemented with a bus architecture,represented generally by the bus 1124. The bus 1124 may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system 1114 and the overall designconstraints. The bus 1124 links together various circuits including oneor more processors and/or hardware modules, represented by the processor1122 the modules 1102, 1104, 1106 and the computer-readable medium 1126.The bus 1124 may also link various other circuits such as timingsources, peripherals, voltage regulators, and power management circuits,which are well known in the art, and therefore, will not be describedany further.

The apparatus includes a processing system 1114 coupled to a transceiver1130. The transceiver 1130 is coupled to one or more antennas 1120. Thetransceiver 1130 enables communicating with various other apparatus overa transmission medium. The processing system 1114 includes a processor1122 coupled to a computer-readable medium 1126. The processor 1122 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium 1126. The software, when executedby the processor 1122, causes the processing system 1114 to perform thevarious functions described for any particular apparatus. Thecomputer-readable medium 1126 may also be used for storing data that ismanipulated by the processor 1122 when executing software.

The processing system 1114 includes a receiving module 1102 forreceiving a first number of CSI-RS ports corresponding to REs. Thereceiving_(—) module 1102 also receives a second number of virtualantenna ports, the second number being less than or equal to the firstnumber. The receiving_(—) module 1102 also receives CSI-RS on eachvirtual antenna port. The modules may be software modules running in theprocessor 1122, resident/stored in the computer-readable medium 1126,one or more hardware modules coupled to the processor 1122, or somecombination thereof. The processing system 1114 may be a component ofthe UE 650 and may include the memory 660, and/or thecontroller/processor 659.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method of wireless communication, comprising:signaling, to at least one user equipment (UE) compatible with LTErelease 10 or higher, a first number of channel stateinformation-reference signal (CSI-RS) ports corresponding to resourceelements (REs) of a CSI-RS pattern, the first number of CSI-RS portsbeing greater than a number of physical antenna ports of a base station;signaling, to the at least one UE, a second number of virtual antennaports, the second number being less than or equal to the first number;and transmitting CSI-RS on each virtual antenna port that is to at leasta portion of the Res of the CSI-RS pattern.
 2. The method of claim 1,further comprising: configuring at least one legacy UE with CSI-RS portsmatching the second number; and configuring the at least one legacy UEwith a muting pattern based on the second number so that the legacy UEperforms measurements on a number of REs allocated based at least inpart on at least in part the second number.
 3. The method of claim 1, inwhich the CSI-RS are mapped to at least two REs corresponding to thefirst number of CSI-RS ports.
 4. The method of claim 1, furthercomprising signaling information for a mapping between the first numberof CSI-RS ports and the second number of virtual antenna ports.
 5. Themethod of claim 1, in which the second number is equal to the firstnumber.
 6. The method of claim 1, further comprising configuring the atleast one advanced UE with the first number of CSI-RS ports in at leasttransmission modes 1, 2, 3, 4, 5, 6, 7, 8, or a combination thereof. 7.A method of wireless communication, comprising: receiving, at anadvanced user equipment (UE), a first number of channel stateinformation-reference signal (CSI-RS) ports corresponding to resourceelements (REs), the first number of CSI-RS ports being matched to amuting pattern for at least one legacy UE; receiving, at the advancedUE, a second number of virtual antenna ports, the second number beingless than or equal to the first number; and receiving, at the advancedUE, CSI-RS on each virtual antenna port, the CSI-RS mapped to at least aportion of the REs.
 8. The method of claim 7, further comprising:performing a channel estimation and/or interference measurement usingthe received CSI-RS.
 9. The method of claim 8, in which the receivedCSI-RS are on at least two REs corresponding to the first number ofCSI-RS ports.
 10. The method of claim 8, further comprising evaluatingchannel state information (CSI) based at least in part on the channelestimation and/or the interference measurement.
 11. The method of claim10, in which the CSI is evaluated based on measurements of the firstnumber of CSI-RS ports in at least transmission modes 1, 2, 3, 4, 5, 6,7, 8, or a combination thereof.
 12. An apparatus for wirelesscommunication, comprising: means for signaling, to at least one advanceduser equipment (UE), a first number of channel stateinformation-reference signal (CSI-RS) ports corresponding to resourceelements (REs); means for configuring at least one legacy UE with amuting pattern matching the first number of CSI-RS ports; means forsignaling, to the at least one advanced UE, a second number of virtualantenna ports, the second number being less than or equal to the firstnumber; and means for transmitting CSI-RS on each virtual antenna port,the CSI-RS mapped to at least a portion of the REs.
 13. An apparatus forwireless communication, comprising: means for receiving, at an advanceduser equipment (UE), a first number of channel stateinformation-reference signal (CSI-RS) ports corresponding to resourceelements (REs), the first number of CSI-RS ports being matched to amuting pattern for at least one legacy UE; means for receiving, at theadvanced UE, a second number of virtual antenna ports, the second numberbeing less than or equal to the first number; and means for receiving,at the advanced UE, CSI-RS on each virtual antenna port, the CSI-RSmapped to at least a portion of the REs.
 14. A computer program productfor wireless communication in a wireless network, comprising: anon-transitory computer-readable medium having non-transitory programcode recorded thereon, the program code comprising: program code tosignal, to at least one advanced user equipment (UE), a first number ofchannel state information-reference signal (CSI-RS) ports correspondingto resource elements (REs); program code to configure at least onelegacy UE with a muting pattern matching the first number of CSI-RSports; program code to signal, to the at least one advanced UE, a secondnumber of virtual antenna ports, the second number being less than orequal to the first number; and program code to transmit CSI-RS on eachvirtual antenna port, the CSI-RS mapped to at least a portion of theREs.
 15. A computer program product for wireless communication in awireless network, comprising: a non-transitory computer-readable mediumhaving non-transitory program code recorded thereon, the program codecomprising: program code to receive, at an advanced user equipment (UE),a first number of channel state information-reference signal (CSI-RS)ports corresponding to resource elements (REs), the first number ofCSI-RS ports being matched to a muting pattern for at least one legacyUE; program code to receive, at the advanced UE, a second number ofvirtual antenna ports, the second number being less than or equal to thefirst number; and program code to receive, at the advanced UE, CSI-RS oneach virtual antenna port, the CSI-RS mapped to at least a portion ofthe REs.
 16. An apparatus for wireless communication, comprising: amemory; and at least one processor coupled to the memory, the at leastone processor being configured: to signal, to at least one advanced userequipment (UE), a first number of channel state information-referencesignal (CSI-RS) ports corresponding to resource elements (REs); toconfigure at least one legacy UE with a muting pattern matching thefirst number of CSI-RS ports; to signal, to the at least one advancedUE, a second number of virtual antenna ports, the second number beingless than or equal to the first number; and to transmit CSI-RS on eachvirtual antenna port, the CSI-RS mapped to at least a portion of theREs.
 17. The apparatus of claim 16, in which the at least one processoris further configured: to configure at least one legacy UE with CSI-RSports matching the second number; and to configure the at least onelegacy UE with a muting pattern based at least in part on the secondnumber so that the legacy UE performs measurements on a number of REsallocated based at least in part on the second number.
 18. The apparatusof claim 16, in which the CSI-RS are mapped to at least two REscorresponding to the first number CSI-RS ports.
 19. The apparatus ofclaim 16, in which the at least one processor is further configured tosignal information for a mapping between the first number of CS-RS portsand the second number of virtual antenna ports.
 20. The apparatus ofclaim 16, in which the second number is equal to the first number. 21.The apparatus of claim 16, in which the at least one processor isfurther configured to configure the at least one advanced UE with thefirst number of CSI-RS ports in at least transmission modes 1, 2, 3, 4,5, 6, 7, 8, or a combination thereof.
 22. An advanced user equipment(UE) configured for wireless communication, comprising: a memory; and atleast one processor coupled to the memory, the at least one processorbeing configured: to receive a first number of channel stateinformation-reference signal (CSI-RS) ports corresponding to resourceelements (REs), the first number of CSI-RS ports being matched to amuting pattern for at least one legacy UE; to receive a second number ofvirtual antenna ports, the second number being less than or equal to thefirst number; and to receive CSI-RS on each virtual antenna port, theCSI-RS mapped to at least a portion of the REs.
 23. The apparatus ofclaim 22, in which the at least one processor is further configured toperform a channel estimation and/or interference measurement using thereceived CSI-RS.
 24. The apparatus of claim 23, in which the receivedCSI-RS are on at least two REs corresponding to the first number ofCSI-RS ports.
 25. The apparatus of claim 23, in which the at least oneprocessor is further configured to evaluate channel state information(CSI) based at least in part on the channel estimation and/or theinterference measurement.
 26. The apparatus of claim 25, in which theCSI is evaluated based on measurements of the first number of CSI-RSports in at least transmission modes 1, 2, 3, 4, 5, 6, 7, 8, or acombination thereof.